PC-SPES was taken off the market because some batches were found to contain prescriptionmedicines in addition to the herbs. Clinical trials of PC-SPES that were underway were stopped. There are products being sold now as substitutes for PC-SPES, but they are not the same mixture. Since the only company licensed to make PC-SPES is no longer in business, PC-SPES is not legally available in the United States.

What is the history of the discovery and use of PC-SPES as a complementary and alternative treatment for cancer?

Most of the herbs in PC-SPES have been used in traditional Chinese medicine (TCM) for many health problems, including prostate problems, for hundreds of years. A chemist in New York and a doctor/herbalist in China worked together to create the mixture. In 1997, a company was formed to make PC-SPES and sell it in the United States without a prescription. Interest in PC-SPES grew, and researchers began looking at it. Tests found that some batches of PC-SPES contained one or more of the following drugs, which are not found in nature:

Because these drugs are to be used only by prescription and could be harmful to some people, PC-SPES was taken off the market in 2002.

What is the theory behind the claim that PC-SPES is useful in treating cancer?

In lab tests, each herb used in PC-SPES has been reported to help keep cancercells from growing or to help prevent cell damage that can lead to cancer and other diseases.

PC-SPES was reported to slow the growth of prostate cancer but did not cure it. It is not known how PC-SPES works in the body. Some of the herbs in the mixture contain phytoestrogens, which are estrogen-like substances found in plants. Estrogen can cause the testicles to stop making testosterone, which makes some prostate cancers grow. Patients' responses to PC-SPES were similar to responses to estrogen therapy using DES. The DES found in some batches of PC-SPES, however, may not have been enough to cause all of the estrogen-like effects that were seen in users of the mixture. There is some evidence that the mixture works in a different way than DES does, and that PC-SPES alone (without DES in it) may fight prostate cancer.

PC-SPES has also shown anticancer effects on prostate cancers that do not depend on testosterone and on other types of cancer. This suggests that PC-SPES may have anticancer qualities other than its estrogen-like effects.

Have any preclinical (laboratory or animal) studies been conducted using PC-SPES?

Studies of PC-SPES in test tubes and using rats showed that it might keep cancer cells from growing. These studies were done, however, before it became known that some batches of the product contained unlisted prescription medicines. Also, the product was not standardized (different batches of PC-SPES were found to contain different strengths of the herbal ingredients). For these reasons, the results of the lab tests and animal studies are not considered to be good evidence.

Have any clinical trials (research studies with people) of PC-SPES been conducted?

Clinical trials of PC-SPES had begun before the product was taken off the market. In these trials, PC-SPES was reported to improve quality of life, reduce pain, and lower PSA (prostate specific antigen) levels in patients with prostate cancer. Rising PSA levels can be a sign that prostate cancer is growing.

After it was learned that some batches of PC-SPES contained prescription medicines, ongoing studies were stopped and previous study results came into question. The responses reported in the studies may have been caused by the prescription medicines that were in the PC-SPES, as well as by the herbal ingredients. Also, since different batches of PC-SPES contained different ingredients, the studies cannot easily be compared.

Have any side effects or risks been reported from PC-SPES?

Common side effects were the same as those reported with estrogen therapy: